The first musical box, created in 1796 by Antoine Fabre, was formed of a cylinder provided with pins and a set of tongues defined as a musical pin-barrel. When the cylinder rotates, the pins on the cylinder are arranged to lift and then release, in a well defined order, the steel tongues of the pin-barrel, which are perfectly tuned, to reproduce a tune. As they fall again, the tongues vibrate and thus each indirectly produce one sound from a melody to be played.
This type of musical box with the aforementioned sound producing device can be integrated in jewellery boxes or in toys or also in watches.
U.S. Pat. No. 2,755,697 may be cited in this regards, which discloses a tongue carried by a comb, which is clamped between a support piece and a clamp.
To adjust the acoustic frequency produced by the tongue, a load member can be added to said tongue. This load member is movable and, depending on the position of said load member along said tongue, the frequency and therefore the sound produced is modified.
U.S. Pat. No. 3,013,460 discloses a set of tongues connected by a common comb. The comb is immobilised on a base, where it is supported and held by a clamp using screws traversing the clamp and the comb. To tune the tongues, instead of adding a load member, the tongues are machined in order to remove material.
To secure this set of tongues of different lengths to a support or a base, a clamp is usually used, which is applied to the comb and which is held in place by screws, whose shafts traverse pierced holes in the clamp and the comb and each cooperate with a threaded sink, comprised in the support. The clamp only presses on the comb and the pierced holes are made to the diameter of the screw shafts with operating play.
In principal, the tongue lengths are calculated each to produce a determined frequency of a sound and no action is necessary in terms of an adjustment. However, as indicated above, it is possible to adjust the vibration frequency of each tongue by adding a load member to the tongue in U.S. Pat. No. 2,755,697 or by removing material in U.S. Pat. No. 3,013,460. This is then a fine adjustment.
The solution of U.S. Pat. No. 2,755,697, of adding a sliding load member, is difficult to implement in the case of a device for incorporation in a watch, due to the miniaturisation required. Further, it is unreliable, as it is difficult to secure the load member to the tongue, given than the vibrations tend to unscrew the screw securing the load member.
The solution set out in U.S. Pat. No. 3,013,460 is more reliable, but requires subjecting the pin-barrel to a further machining operation.
Beyond these fine adjustments, when it is desired to work in a different frequency range, another pin-barrel has to be produced with different tongue lengths. A pin-barrel having its own tongue lengths must thus be produced each time, which is a drawback.